1. Field of the Invention
This invention relates to a binocular-type viewing system having a substantially enlarged field of view that can be used preferably in low light and low gravity conditions.
2. Discussion of Related Art
Existing night vision systems have many applications in every day life. Perhaps the most well known use for night vision systems is by the military when performing night time maneuvers. The night vision systems permit vision under very low light conditions by converting incoming infrared and/or visible light from a viewed scene to an intensified visible light image. During night time maneuvers, military personnel are often performing other tasks, such as piloting an aircraft or driving a vehicle, which require the freedom of their hands while they are scanning the territory. Accordingly, night vision systems have been developed to be worn upon the head of a user, such as goggles being secured directly on the head or by being mounted to a helmet or a visor.
Placing a night vision system on the head of a user places significant constraints upon the optical design of the system. For example, goggles worn upon the head of a user must be both compact and light in weight because excessive weight or front-to-back length of the goggles can cause the goggles to exert large moments on the user's head causing severe instability problems and preventing their effective use in applications in which the user's head may be subjected to high gravitational or centrifugal loads. Furthermore, in a wide field of view optical system, the focal length of the eyepiece optics must be shortened correlatively that of the wide angle objective for unity magnification; and, in night vision goggles, this results in insufficient eye relief between the eyepiece optics and the eye, which not only causes discomfort to the user, but also interferes with the ability to position a helmet visor, eyeglasses and other structures between the goggles and the eyes of the user. In order to compensate for inadequate eye relief, prior night vision goggles have generally been limited to providing a field of view of no more than about 40 degrees.
Night visions goggles have been used in military aviation for several years with fields of views ranging from 30 degrees (Early Cat's Eyes night vision goggles from GEC-Marconi Avionics) to 45 degrees (NITE-OP and NITE-Bird night vision goggles, also from GEC-Marconi Avionics). The vast majority of night vision goggles used in military aviation have a 40 degree field of circular view (AN/AVS-6 and AN/AVS-9). A major limitation of such prior art devices is that increased field of view could only be obtained at the expense of resolution since each ocular uses only a single image intensifier tube and each image intensifier tube has a fixed number of pixels. Therefore, if the fixed numbers of pixels is spread over a larger field of view, then the angular subtense per pixel increases, which translates into reduced resolution. Understandably increased field of view is a major enhancement desired by military aviators, closely followed by resolution. In conventional goggles, both eyes also typically see the same field of view, i.e., there is a 100-percent overlap of the image viewed by both eyes of the observer. Such a limited field of view greatly restricts the effectiveness of the night vision apparatus.
U.S. Pat. No. 5,229,598 addresses the above-mentioned problems and discloses a compact, lightweight, night vision system capable of providing an enlarged field of view of up to 60 degrees with improved visual acuity and sufficient eye relief.
In addition to night vision systems, other imaging systems, such as handheld binoculars, typically provide a rather limited field of view; and it would be desirable to provide such systems with increased fields of view as well.